The present invention relates to a float arm assembly used for measuring the liquid level in a fuel tank, and in particular to a float arm assembly in a vehicle fuel tank.
A typical float arm assembly used in a vehicle fuel tank includes a fixed support to which a ceramic resistor card is mounted. A float is pivotally mounted to the resistor card by a float arm. As the fuel level in the tank goes up and down, the buoyancy of the float causes it to move up and down with the level of fuel, thus changing the angle of the float arm relative to the resistor card. This change in angle causes a change in output from the resistor card, which is typically received and processed by a powertrain control module and displayed on the fuel gauge.
In modern automotive vehicles, the desire to maximize the capacity of a fuel tank may require the fuel tank to have a greatly contoured shape. This may even include significant indentations in the fuel tank wall in order to avoid adjacent vehicle structure and components. The contoured shape—in combination with the indentations—may limit the amount of pivoting of the float and float arm that can occur without creating interference problems between the float arm assembly and the fuel tank wall. Consequently, the float and float arm may not be able to pivot all the way up to a full liquid level and/or all the way down to an empty liquid level. Such limitations in the travel of the float arm and float, then, create a dead band, which is the unreadable but useful fuel in the fuel tank. This dead band is undesirable because it limits the accuracy of the fuel gauge reading, which may reduce customer satisfaction with the vehicle and possibly even increase warranty costs.
Attempts to minimize the dead band have included fuel tanks with two separate float arm assemblies, each mounted and operating separately. While this may reduce dead band concerns, it adds an additional sender opening for communicating the additional fuel level signal to the powertrain control module. This multiple float arm assembly, then, requires the powertrain control module to receive and process a second, separate fuel level signal, adds additional cost for fabricating and assembling an entire separate float arm assembly and cover for the second sender opening, and increases the potential for permeation out of the tank.